Try it out

Download the secondary-image (external: https://imgur.com/a/bt5Ozx7),
visit https://gabriellesc.github.io/piet/
"Import" the image.
On the right side, there is a "Debugger"-tab.
Click it, and press the green triangle to start the program.
The website will show a little animation while going through each code segment.

(PIET debugger is written by Gabrielle Singh Cadieux, 2018)

About

Have you every wondered, how you could write letters in the most difficult manner? Try the PIET programming language then! ^^'

PIET is an esoteric visual programming language. Each Pixel is read and turned into code clockwise. The code depends not on the color, but on the color transition.
Keeping the tone, but going darker in the next pixel, pushes the number of preceding pixels with the same color to the stack. Then you do some math to calculate the ASCI code of a letter, but in assembler fashion, and print it out.

For example, "H" has code 72 = 8 * 9 = ( 4+4 ) * ( 3*3 ), so in assembler you write
[4] [PUSH] [DUP] [+] [3] [PUSH] [DUP] [*] [*] [OUT]
And you get a "H". ^^

Typically, you use [DUP] to preserve a copy, so from "e" to "a" you only need [DUP] [4] [-] [OUT] instead.

There are three interesting aspects to this language:

You can hide programming code in images visually
By rotating the colors or changing the resolution, you can have completely different images leading to the same assembler code
You can calculate PI by drawing a circle. The larger the image (pixels) the more precise is the result (Area divided by radius squared)

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